Police arrested another union leader of the state-run rail operator on Friday as part of their investigation into an ongoing controversial strike by thousands of unionized workers, which the government calls illegal.

With a court-issued warrant, police arrested the union leader of the state-run Korea Railroad Corp. (KORAIL), only identified by his surname Koh, in Daejeon, 150 kilometers south of Seoul, after days of tracking him down.

More than 6,500 unionized KORAIL workers walked off the job for the 12th day in protest against a government decision to set up a KORAIL subsidiary to run part of the high-speed train services. The union suspects the move would ultimately lead to its privatization.

The union head Kim Myung-hwan was the first to be apprehended on Thursday after district courts across the country issued warrants for 25 strike leaders for refusing to respond to summons by prosecutors.

Amid the prolonged strike, the management gave an ultimatum to the union, ordering striking members to return to work.

The company reiterated that the subsidiary's establishment has nothing to do with privatization, saying that the new unit will be owned by KORAIL and state-run investors.

The new service will run from Suseo-dong in southern Seoul to the southern provincial city of Busan. After several delays, it is expected to begin operations in 2016.

Despite the union's request to delay issuing a state license for the new rail service, the government said it will grant the license as planned later in the day. (Yonhap News)